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Re: panic on 4.20 server exporting xfs filesystem

To: Christoph Hellwig <hch@xxxxxx>
Subject: Re: panic on 4.20 server exporting xfs filesystem
From: "J. Bruce Fields" <bfields@xxxxxxxxxxxx>
Date: Thu, 19 Mar 2015 14:47:14 -0400
Cc: Dave Chinner <david@xxxxxxxxxxxxx>, Eric Sandeen <sandeen@xxxxxxxxxxx>, linux-nfs@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20150319172731.GA16329@xxxxxx>
References: <54F78BE5.1020608@xxxxxxxxxxx> <20150304225623.GZ4251@dastard> <20150305040849.GJ1627@xxxxxxxxxxxx> <20150305131731.GA16235@xxxxxx> <20150305150138.GA15674@xxxxxxxxxxxx> <20150305170217.GC15674@xxxxxxxxxxxx> <20150305204749.GA17934@xxxxxxxxxxxx> <20150305205922.GF18360@dastard> <20150306204715.GA27257@xxxxxxxxxxxx> <20150319172731.GA16329@xxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Thu, Mar 19, 2015 at 06:27:31PM +0100, Christoph Hellwig wrote:
> FYI, I've now managed to reproduce the issue.  I haven't had time
> to dig deeper, but it smells a lot like a callback path issue.
> 
> Can you send the recursion fix to Linus ASAP and I'll send you a patch
> to turn the nopnfs option into a pnfs one, so we're at least doing
> fine for 4.0 in any case.

Sure, sounds good.

Also, there's the problem that when this is turned on a client can end
up doing unnecessary LAYOUTGET.  Do we have a plan for that?

Possibilities:

        - Just depend on export flags: but some clients may have direct
          access and some not.  If the clients with direct access or all
          easily identifiable by IP subnet, maybe it's not a big deal.
          Still, seems like an administrative hassle.

        - Do nothing, assume the client can deal with this with some
          kind of heuristics, and/or that the GETLAYOUT calls can be
          made very cheap.  Not sure if that's true.

        - Use something like GETDEVLICELIST so the client can figure out
          in one go whether any layouts on a given filesystem will work.
          I forget what the problems with GETDEVICELIST were.

> I hope to debug this and may even have
> a real fix soon, but so far I don't know how long it will take.

OK, thanks.

--b.

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